For years, the public switched telephone network of the U.S. has provided reliable two-way telephone service. This network is made up of various types of well-known switching systems and well-known physical media over which are carried electrical signals representing voice-frequency information.
Those skilled in the art know that switching systems of the public switched telephone network synchronously route electrical signals in the form of bi-polar, binary-valued pulses that represent samples of voice frequency information. Telephone conversations, which by their nature require immediate transmission, are adequately carried over synchronous networks, which, by definition, carry data at a fixed rate. In addition to carrying digitized voice communications however, the public switched telephone network also carries data of the kind that is created and used by computers.
While the synchronous public switched telephone network provides very reliable communications for both voice and data, there are now several different kinds of asynchronous data networks that are intended to carry primarily data (not necessarily representing speech) but which are now being considered to carry telephone calls much as the public switched telephone network does. Some of these data networks include Ethernet networks, asynchronous transfer mode (or “ATM”) networks, Internet protocol (or “IP”) networks and frame relay networks, among others. They all share a few characteristics: data is sent in discrete bundles or packets and the packets are sent asynchronously as opposed to synchronously.
In order to carry acceptable voice quality telephone calls or voice traffic, which require near-zero latency variation between the voice sample transmissions, an asynchronous network must be set up so as to allow digitized voice samples to be reliably and repeatedly routed through the network and delivered to a destination on time so that a person's utterances that are reconstructed from recovered data packets is at least a reasonable facsimile of the speaker's actual voice. Inasmuch as those skilled in the art know that any band-limited time-varying signal that is sampled at a sufficiently high rate can be perfectly reconstructed from the samples but only if all of the samples are delivered and delivered on time and in the proper sequential order, dropping or losing data samples that represent an analog signal will degrade the reproduction quality of digitized signal. When voice samples are carried over an asynchronous network, even delaying a voice sample will degrade signal reproduction. As voice samples are delayed or lost on an asynchronous data network, reproduction quality gets increasingly worse. A method and apparatus by which the transmission quality of service through an asynchronous network might be measured might be a valuable tool in insuring voice quality when an asynchronous network is used to carry telephone traffic.